During cold start conditions, a liquid such as oil within a heat exchanger can be subject to very low temperatures. These low temperatures can cause the oil to have a very high viscosity, which in turn can cause the oil to congeal. The congealed oil causes high pressure losses in the system which can lead to the heat exchanger system seizing up. To mitigate these conditions, warm inlet oil can be passed through the heat exchanger to warm the cold oil inside and heat it up, thereby reducing its viscosity and allowing it to flow more freely.
To this end, a de-congealing channel may be provided to supply warm oil to the heat exchanger matrix. Such an arrangement places limitations on the geometry and construction of the heat exchanger.